Scientists have found structures that resemble an emu's red blood cells inside eight 75 million-year-old dinosaur bones, suggesting the ancient animals' fossils may hold more secrets than we realized.

The bones included a theropod claw, possibly from Gorgosaurus. (Photo: Kabacchi/Flickr)

Bones have taught us a lot about dinosaurs over the past century, revealing a tantalizing story of bizarre animals no human has ever seen alive. And the plot may be thickening, thanks to hints of soft tissue — including structures akin to collagen and emu-like blood cells — found in eight dinosaur fossils.

While bone can stay intact for hundreds of millions of years, soft tissue tends to break down more quickly. All traces are usually gone within a million years or so, although it can last longer in certain conditions — possibly including the interior of dinosaur bones, as the new study suggests. It's not quite "Jurassic Park," but it's still raising hopes for a renaissance in our understanding of dinosaurs.

"We still need to do more research to confirm what it is that we are imaging in these dinosaur bone fragments, but the ancient tissue structures we have analysed have some similarities to red blood cells and collagen fibres," says lead author Sergio Bertazzo, a researcher at Imperial College London, in a statement about the discovery. "If we can confirm that our initial observations are correct, then this could yield fresh insights into how these creatures once lived and evolved."

Scientists have found signs of soft tissue in dinosaur fossils before. Some bones and tracks end up with skin impressions, and a 2005 study reported soft tissue in 68 million-year-old Tyrannosaurus rex bones, a finding some critics attributed to contamination rather than T. rex tissue. But the new study not only seems to support dino origins; it suggests such tissue might be more common than we thought.

That's partly because it comes from such low-quality bones. Previous signs of soft tissue came from well-preserved dinosaurs, yet this study used new imaging techniques to study shabby fossil fragments unearthed more than a century ago. If those 75 million-year-old scraps of rib, claw and tibia still hold soft tissue, similar clues about dinosaur biology could be hiding in museums around the world.

The Cretaceous Period fossils were found early last century in Alberta, Canada, and eventually ended up at the Natural History Museum in London. They include one theropod claw, a Chasmosaurus rib, a toe bone from a triceratops relative and various bones from hadrosaurs.

"It's really difficult to get curators to allow you to snap bits off their fossils," study co-author and Imperial College paleontologist Susannah Maidment tells the Guardian. "The ones we tested are crap, very fragmentary, and they are not the sorts of fossils you'd expect to have soft tissue."

The researchers used several methods to study the tissue, including a scanning electron microscope, a transmission electron microscope and a focused ion beam, which helped them slice cleanly into the fossils. In at least two bones, they found structures that look like red blood cells, also known as erythrocytes. It's still not clear what these are, but they seem to have a nucleus, and since mammalian red blood cells lack nuclei, the researchers doubt it's human contamination.

Using an ion mass spectrometer, they realized the structures bear a resemblance to red blood cells from an emu. Birds are descendants of dinosaurs, as any "Jurassic Park" fan knows, and these flightless Australian birds are seen as one of the closest modern-day analogues of their extinct ancestors. That seems to suggest this is dinosaur blood, which could shed new light on how dinosaurs evolved a warm-blooded metabolism. But contamination can't be ruled out yet, Bertazzo tells the Verge.

"Even if it is quite unlikely that someone or some bird cut themselves and bled on the fossil at any point in time and right on the spot we took the smaller bit off, this is always a possibility," he says.

The researchers also found fibrous structures with a banding pattern similar to collagen, the main protein in connective tissue. The structure of collagen varies among different animal groups, so its presence in dinosaur bones could help scientists understand how various types of dinosaurs are related.

It's hard to hear about preserved dinosaur blood without John Williams' "Jurassic Park" theme swelling in the back of your mind — especially since this study came out just a few days before the U.S. release of "Jurassic World." The researchers urge caution, though, noting that dinosaur DNA has yet to be found. According to a 2012 study, DNA has a half life of 521 years, meaning it should only last up to 6.8 million years at best. The last dinosaurs died out about 65 million years ago.

"Although we have found dense internal structures that we have interpreted as nuclei in our cells, and the cells we found appear to preserve original components of blood, there is no evidence of any organelles or DNA within the nuclei," Maidment tells Reuters. "But even if one was to find some fragments of DNA, we would not be able to reconstruct a dinosaur 'Jurassic Park'-style because we would need the complete genome to figure out where the holes in the DNA are."

Still, life finds a way, as Dr. Ian Malcom famously put it. And as Maidment points out to the Guardian, science often does, too. "We haven't found any genetic material in our fossils," she says, "but generally in science, it is unwise to say never."